There are many light or heavy pipes in ships, plants, piping work sites and the like. That is, pipes through which various fluids, gases, electrical connections or the like might pass are installed as complicatedly as cobwebs.
In reality, since such pipes are limited in length, a welding operator welds a plurality of pipes to one another to make the pipe in a desired length.
Particularly, even a single pipe used in main pipe lines and the heavy weight pipes are interconnected to be made into relatively long pipes while being suitable for a pipe line or plumbing design.
Herein, a reference pipe (hereinafter, referred to as ‘first pipe’) and a pipe (hereinafter, referred to as ‘second pipe’) corresponding to an object to be aligned and which is to be butt-welded to the first pipe, are required to be aligned before a butt weld.
A user performs a leveling operation by manually adjusting the direction, location and height of the second pipe by use of a wire or belt of a crane, thereby making the first pipe and the second pipe aligned.
The user puts the first pipe in a table like a surface plate, and puts the second pipe in a simple jig like a Y block placed in a location opposite to the surface plate. The simple jig supports the second pipe in the lower portion of the second pipe and acts to fix the second pipe by the self weight of the second pipe and the Y block.
The user moves the second pipe little by little in all directions of motion forward, backward, left, right, upward, downward and the like after lifting the second pipe slightly with the wire of the crane, or adjusts the height and direction of the simple jig in accordance with the movement, thereby aligning the second pipe to the first pipe.
However, the manual pipe aligning operation like this is very difficult when the second pipe is long in length and heavy in load, and includes a disadvantage in that an operation time for aligning and welding the pipes takes long depending on the height, angle, location, vibration and the like of the pipe even if the operator is a skilled one, especially when there is an imbalance state such that the center of gravity is eccentric from the center of volume according to the shape of the second pipe.
Further, the welding operation of the pipe cannot be performed quickly because of the difficulty to perform the manual pipe aligning operation in a precise manner. For example, during the welding operation for welding the first and the second pipe, an operator is typically required to go inside of the pipe to tack-weld the joining portion, and then welds the pipe from outside in a regular manner.
Accordingly, there is required a weight balancer that can improve weld quality by precisely adjusting the height, location, inclination, vibration of the pipe, as 6 degrees of freedom is given to a double plate type of operation plate supporting the pipe.
Further, generally, a plurality of pipes is required to be aligned for being interconnected before the butt weld. The combining operation before the butt weld of the two pipes according to the prior art is as follows. The combining operation is that the gap and stepped difference between the preset pipes are made to meet with a specific tolerance so as to weld the pipes by, e.g., TIG. Here, roundness correction should be made for the two pipes to be fitted consistently to each other.
Herein, a true circle refers to a circle of which the diameter or radius measured along the circumference is fixed. In regards to a pipe, the true circle further refers to a circle where the roundness corresponding to the difference between the maximum inside diameter and the minimum inside diameter is set within a tolerance.
In the pipe joining method of the prior art, the operator puts all the pipes on the surface plate and uniformly maintains their gaps to be in contact with one another by using the wire or the belt, and then a tack weld is performed by joining a first tab piece to one side of the external diameter of the pipe. Then, the operator inserts a power jack into the pipe and makes the stepped difference fitted while correcting the true circle of the pipe in use of the power jack repeatedly, and then the tack weld is performed to join a second tab piece to the opposite side of the pipe having the first tab piece attached thereto which was joined first. After then, the operator continuously tack-welds in order to join a third tab piece to a location corresponding to a 90° direction of the second tab piece of the pipe, followed by an operation of joining a fourth tab piece to an opposite side of the pipe having the third tab piece attached thereto. Then, the operator corrects the gap of the pipe by moving a spatula chisel in the circumference of the pipe after inserting the spatula chisel into the gap between the two pipes. Finally, the operator further joins other tab pieces between the first and the second tab piece, between the second and the third tab piece, between the third and the fourth tab piece and between the fourth and the first tab piece by tack-welding. Here, the number of other tab pieces is determined by diameters of pipes.
However, the pipe joining operation according to the prior art includes a problem in that the operation time does not only consume a lot of time as it is progressed manually, but the deviation of the weld quality is also very inconsistent depending on the proficiency of the operator. Thus, there is a disadvantage in that, when the pipe joining operation is not performed in a smooth manner, it affects the subsequent welding operation for the pipe at later.
Further, the pipe joining operation according to the prior art is more difficult when the pipe is large. That is, one large pipe is put on the surface plate, and in order to connect to the large pipe after that, another large pipe is put on a plurality of jigs having the same height as the level of the surface plate in use of the crane. After then, the operator corrects the gap by inserting the wire between the two large pipes while manipulating the crane, adjusting the height of the jig or moving them left and right, and meets the stepped difference by temporarily installing a level on the top thereof, and then, the tab pieces are fixed from the top by the tack weld method. After then, the tab piece is tack welded thereunder after correcting the stepped difference and the true circle by inserting a power jack into the pipe. After then, the remaining tab pieces are welded around the circumference of the pipe.
However, the pipe joining operation according to the prior art includes an inconvenience in that the large pipe should be moved in use of the transport device like a separate crane for correcting the roundness because the large pipe includes an excessive weight, e.g., about 600 kg, and a length, e.g., about 6 m, and includes a disadvantage in that the operation time of aligning and welding the pipes takes long due to the height, angle, location, vibration and the like of the pipe even though the operator is highly skilled because there is an imbalance state such that the center of gravity is eccentric from the center of volume in accordance with the shape of the pipe, e.g., bent pipe, elbow, T-pipe and the like.
Further, in order to prevent oxidization and nitrification in the welding process, expensive argon (Ar) gas is injected into all the space within the pipe, and the injected argon gas is discharged to the air through an opening portion of both side ends of the pipe, thus there is a problem in that a gas pursing cost is increased.
In order to solve the above, the present applicant has proposed an automatic pipe aligning device and a pipe aligning method, as disclosed in Korea Patent No. 639607 (referred to as ‘Patent Reference 1’).
However, there has been found a difficulty with regards to the automatic pipe aligning device of the Patent Reference 1 in aligning pipes while overcoming the weight of a fitting portion of one pipe to be aligned to another pipe.
For example, in case that the weight and length of the pipe corresponding to the fitting portion is about 600 kg and 6 m, there occurs a case that the six degrees of freedom motion is not realized because a six axis parallel robot like stewart-gough platform installed within the automatic pipe aligning device cannot support the weight of the fitting portion, thereby failing to align or fit the pipes. Herein, the six degrees of freedom motion includes a three-axis translational motion and a three-axis rotational motion. Here, the three-axis translational motion includes forward and backward motion (Surge) of X-axis direction; left and right motion (Sway) of Y-axis direction; up and down motion (Heave) of Z-axis direction, and the three-axis rotational motion includes rolling (ro) in which it rotates on the basis of X-axis direction; pitching (pi) in which it rotates on the basis of Y-axis direction; and yawing (ya) in which it rotates on the basis of Z-axis direction.
Further, in order to align a small fitting portion, the six axis parallel robot can move the fitting portion to the pipe, but friction occurs between the upper portion of the weight balancer and the fitting portion. Thus, an excessive load might be given to the fitting portion and the automatic pipe aligning device, there might occur damages such as scratch and the like in the fitting portion, and the clamping location of the automatic pipe aligning device and the fitting portion might be changed.
Further, the automatic pipe aligning device of the prior art does not consider a co-operative operation with a separate weight balancer, but only proposes the automatic pipe aligning method by the automatic pipe aligning device, thus in fact there occurs much difficulty in automatically aligning pipes because there was no mention for the method of joining them together with the weight balancer.
For example, the automatic pipe aligning method of the prior art includes a disadvantage in that the clamping location is unstable and the precision of correcting the true circle or of aligning the pipe and the fitting portion is relatively low because no action is disclosed for balancing the device right before clamping.
Particularly, the weight balancer mentioned in the description of the automatic pipe aligning device of the prior art includes a simple structure. The fitting portion which is aligned to the pipe is mounted on the upper portion and the weight balancer moves on the ground to act to form a joint portion by putting the fitting portion into contact with the pipe.
However, in case that the weight balancer is used in the automatic pipe aligning device of the prior art, a load for the fitting portion which is a payload cannot be reduced actively, and cannot support the fitting portion while translationally moving or rotating to correspond to the 6 degrees of freedom. Further, the upper portion of the weight balancer supporting the fitting portion is fixed, thereby resulting in a problem that the friction is generated, as mentioned above, between the fitting portion and the upper portion of the weight balancer.